Drupal 8 can concatenate assets like CSS and JS. This can greatly reduce the amount of HTTP request. But with HTTP2 the overhead of an HTTP request is now very low and concatenation seem useless and can degrade performances.
Perhaps the first step would be to create a notice in admin/reports/status if you a in HTTP2 and use bandwidth optimization for assets.
There is a lot to explore like server push and content prioritization. Peoples have to understand that HTTP2 turn best practices upside down.